Clinical Biomechanics - Articles in Press

Measurement of stiffness changes in immobilized muscle using magnetic resonance elastography - Corrected Proof

2010-03-17

Abstract: Background: The isolated evaluation of changes in muscle following immobilization and disuse is a challenge in living subjects. The purpose of this study was to determine whether magnetic resonance elastography is capable of detecting these changes.Methods: An animal model was created to produce a mild joint contracture following 42days of one forelimb immobilization in a maximally flexed position with twice-daily passive exercise. Eight pairs of dog forelimbs were harvested. Magnetic resonance elastography scans were performed on the experimental limb in an extended elbow position with a torque of 0.6Nm. Scans of the contralateral limb were performed in two conditions, position matching and torque matching. Furthermore, wet weight, cross sectional area, resting muscle length, and range of elbow joint motion were measured.Findings: The muscle from the experimental limb showed significant reduction in muscle mass, cross sectional area, slack length, and range of elbow motion. When comparing limbs in position matching condition, the muscle lengths were similar, and the experimental muscle had a significantly higher shear modulus (79.1 (SD 12.0)kPa) than the contralateral muscle (31.9 (SD 24.4)kPa). When comparing limbs in torque matching conditions, the muscle strains were similar, and the experimental muscle had a significantly lower shear modulus than the contralateral muscle (113.0 (SD 24.8)kPa).Interpretation: These findings suggest that following immobilization, magnetic resonance elastography has the potential to be used as a clinical tool to guide rehabilitation and as a research tool to study the loss of passive elastic components of muscle.

Prolonged activity of knee extensors and dorsal flexors is associated with adaptations in gait in diabetes and diabetic polyneuropathy - Corrected Proof

2010-03-08

Abstract: Background: People with diabetes or diabetic polyneuropathy often experience limitations in mobility and gait. These limitations are believed to be related to disturbed muscle function and sensory information. In previous studies on diabetic gait, results were confounded by a lower, preferred walking speed in people with diabetes or diabetic polyneuropathy. This study aimed to identify gait-velocity independent effects of diabetes and diabetic polyneuropathy on lower extremity kinematics and muscle activation patterns.Methods: Eight people with diabetic polyneuropathy, 10 diabetic controls without polyneuropathy and ten healthy, age-matched controls walked at their preferred velocity and a standard velocity of 1.4ms−1. Muscle activation patterns of gluteus maximus, biceps femoris, rectus femoris, vastus medialis, gastrocnemius medialis, soleus, and tibialis anterior, and spatiotemporal and joint angles characteristics were analysed.Findings: Independent of walking speed, muscle activation differed between groups. In diabetic polyneuropathy participants activation of ankle-joint dorsal flexors was prolonged by 5–10% of the stride cycle. Activity of monoarticular knee-joint extensors lasted about 10% longer in both diabetic groups compared to healthy elderly. Initiation of muscle activity did not differ between groups. If gait velocity was controlled, spatiotemporal characteristics were similar between groups.Interpretation: The study showed that independent of the preferred lower gait velocity, people with diabetes or diabetic polyneuropathy adjust the timing of muscle activity. Contrarily, the concurrent changes in spatiotemporal characteristics occurred to be the result of changed velocity only. The delayed cessation of muscle activity suggested a reduced rate of force development underlying the adjusted timing of muscle activation.

Does stride length influence metabolic cost and biomechanical risk factors for knee osteoarthritis in obese women? - Corrected Proof

Elizabeth M. Russell, Barry Braun, Joseph Hamill — 2010-03-03

Abstract: Background: Obesity is the primary modifiable risk factor for knee osteoarthritis. The goal of this study was to develop a walking protocol for obese individuals that supported weight loss while minimizing biomechanical risk factors for knee osteoarthritis. We tested the hypotheses that walking with short, quick strides at a preferred walking speed requires more energy expenditure in obese women and reduces biomechanical risk factors for knee osteoarthritis at foot–ground impact relative to walking at the preferred stride length.Methods: Ten obese (BMI=33.09(4.22)kg/m2) and 10 healthy-weight (BMI=22.66(0.86)kg/m2) women volunteered. was measured while subjects walked on a treadmill at their preferred walking speed at a preferred stride length and a 15% shortened stride length (increased stride frequency). Peak impact shock, peak external knee adduction moment, and knee adduction angular impulse were measured during the two gait conditions.Findings: Decreasing stride length 15% significantly increased metabolic cost by 4.6% (P<0.01; effect size=0.24) and decreased the adduction angular impulse (P=0.046; effect size=0.203), but did not significantly affect the adduction moment (P=0.196; effect size=0.100) or impact shock (P=0.698; effect size=0.605).Interpretation: The small, but significant, increase in metabolic cost when walking with short, quick steps may be beneficial for weight reduction or maintenance in obese populations. The results of this study suggest that a 15% decrease in stride length is not sufficient to decrease the peak values of two of the biomechanical variables that may predispose obese women to knee osteoarthritis but does elicit benefits over the course of a stride.

Mechanobiological regulation of the remodelling cycle in trabecular bone and possible biomechanical pathways for osteoporosis - Corrected Proof

Bríanne M. Mulvihill, Patrick J. Prendergast — 2010-03-02

Abstract: Background: The rapid loss of trabeculae as observed during osteoporosis is attributed to pathological changes in the bone remodelling process. In this study, it is proposed that osteoporosis is due to altered signals resulting from either (i) a decrease in the mechanosensitivity of the sensor cells or (ii) an increase in the bone tissue elastic modulus.Methods: To test these hypotheses, a mechanobiological algorithm was developed and applied to simulate the remodelling cycle in a realistic trabecular strut. The model is based on the supposition that bone resorption is initiated either to remove damaged tissue or when strains fall below a lower threshold; bone formation is triggered when strains exceed an upper threshold.Findings: Applying this algorithm to a realistic trabecula, resorption and subsequent refilling of a cavity was simulated. Results showed that decreases in the mechanosensitivity (simulated by increasing the upper strain threshold) led to under-refilling of cavities. A critical sensitivity was found to exist, above which perforation of the strut due to osteoclastic resorption occurred. It was also found that increases in the bone tissue elastic modulus lead to an increased propensity for trabecular perforation.Interpretation: It may be concluded that if cells become less mechanosensitive, or if increases in the elastic modulus of trabecular bone tissue occurs, the possibility of trabecular perforation and therefore the rapid loss of bone mass increases. If this is true, the preservation of the bone mineral content or maintenance of bone cell mechanosensitivity are potential therapeutic strategies for the prevention of osteoporosis.

Mechanics of the anterior interval of the knee using open dynamic MRI - Corrected Proof

2010-03-02

Abstract: Background: The anterior interval of the knee has been defined as the space between the infrapatellar fat pad and patellar tendon anteriorly, and the anterior border of the tibia and the transverse meniscal ligament posteriorly. Investigation of the normal kinematics of this region is necessary as we begin to appreciate the significant impact that pathologic processes of the anterior interval have on the knee.Methods: Non-weight bearing and weight bearing dynamic MRIs of 20 healthy knees were evaluated at 30° intervals from 0° to 120° flexion. The angle subtended by the patellar tendon and the anterior tibia was measured at each interval of flexion by three independent observers. The amount of angular change over each interval of flexion was also evaluated and the differences between the relative weight bearing conditions were statistically evaluated.Findings: The angle formed by the anterior tibia and the patellar tendon decreases with knee flexion (45.2° (SD 10.1°) at full extension vs. 1.2° (SD 2.1°) at full flexion). The average patellar tendon–tibial angle excursion was significantly reduced with full-weight bearing, 43.1° (SD 11.2°) from 0° to 120° of flexion, compared to non-weight bearing, 30.9° (SD 6.1°) over the same range of motion (P<0.001). Full-weight bearing decreased the angle excursion by 28% compared to non-weight bearing.Interpretation: The observed changes in the anterior interval are influenced by multiple factors including load, knee architecture, tendon elasticity and tibio-femoral and patello-femoral kinematics. The impact of load on the mechanics of the anterior interval is most pronounced between 0° and 30° of flexion.

A three-dimensional parameterized and visually kinematic simulation module for the theoretical range of motion of total hip arthroplasty - Corrected Proof

Wen-Ting Ji, Kai Tao, Cheng-Tao Wang — 2010-03-02

Abstract: Background: Proper option and optimal alignment of implants are major factors in obtaining the desired range of motion of total hip arthroplasty. It would be very useful if a tool is available to assist clinicians to preoperatively determine proper implants and their optimal intraoperative alignment for individual patient.Methods: Based on the secondary development function of ADAMS/VIEW, a three-dimensional parameterized module was developed to simulate six motions of implants for total hip arthroplasty. Total eight parameters (stem abduction, acetabular size, head size, general head–neck ratio, stem–neck angle, acetabular anteversion, acetabular inclination and femoral antetorsion) were included and three definitions of acetabular orientations (operative, radiographic and anatomical) were available. Any initial position of implants and simulation precision could be defined on the demand.Findings: After entering these eight parameters, a special model of total hip arthroplasty would be constructed. Single or combined motion until the prosthetic impingement could be simulated visually and the corresponding maximal rotation angle would be quantified.Interpretation: Clinical factors, such as patients with severe deformity of hip joint or a large range of motion demand, should be considered during total hip arthroplasty. This module can provide references for clinicians on proper option and intraoperative implantation of components, and be suitable for postoperative evaluation. Furthermore, it is a tool to investigate the “safe-zones” of total hip arthroplasty and also can be employed for the design of new implant system.

Achilles tendon length changes during walking in long-term diabetes patients - Corrected Proof

2010-03-02

Abstract: Background: Diabetes leads to numerous side effects, including an increased density of collagen fibrils and thickening of the Achilles tendon. This may increase tissue stiffness and could affect stretch distribution between muscle and tendinous tissues during walking. The primary aim of this study was to examine stretch distribution between muscle and tendinous tissues in the medial gastrocnemius muscle–tendon unit in long-term diabetes patients and control subjects during walking.Methods: Achilles tendon length changes were investigated in 13 non-neuropathic diabetes patients and 12 controls, whilst walking at a self selected speed across a 10m force platform. Electromyographic activity was recorded in the medial gastrocnemius, soleus and tibialis anterior muscles, goniometers were used to detect joint angle changes, and ultrasound was used to estimate tendon length changes.Findings: Achilles tendon length changes were attenuated in diabetes patients compared to controls, and were inversely correlated with diabetes duration (r=−0.628; P<0.05), as was ankle range of motion (r=−0.693; P<0.01). Tendon length changes were also independent of walking speed (r=−0.299; P=0.224) and age (r=0.115; P=0.721) in the diabetic group.Interpretation: Stretch distribution between muscle and tendon during walking is altered in diabetic patients, which could decrease walking efficiency, a factor that may be exacerbated with increasing diabetes duration. Diabetes-induced changes in mechanical tendon properties may be at least partly responsible for attenuated tendon length changes during walking in this patient group.

Foot placement in a body reference frame during walking and its relationship to hemiparetic walking performance - Corrected Proof

Chitralakshmi K. Balasubramanian, Richard R. Neptune, Steven A. Kautz — 2010-03-02

Abstract: Background: Foot placement during walking is closely linked to the body position, yet it is typically quantified relative to the other foot. The purpose of this study was to quantify foot placement patterns relative to body post-stroke and investigate its relationship to hemiparetic walking performance.Methods: Thirty-nine participants with hemiparesis walked on a split-belt treadmill at their self-selected speeds and 20 healthy participants walked at matched slow speeds. Anterior–posterior and medial–lateral foot placements (foot center-of-mass) relative to body (pelvis center-of-mass) quantified stepping in body reference frame. Walking performance was quantified using step length asymmetry ratio, percent of paretic propulsion and paretic weight support.Findings: Participants with hemiparesis placed their paretic foot further anterior than posterior during walking compared to controls walking at matched slow speeds (P<.05). Participants also placed their paretic foot further lateral relative to pelvis than non-paretic (P<.05). Anterior–posterior asymmetry correlated with step length asymmetry and percent paretic propulsion but some persons revealed differing asymmetry patterns in the translating reference frame. Lateral foot placement asymmetry correlated with paretic weight support (r=.596; P<.001), whereas step widths showed no relation to paretic weight support.Interpretation: Post-stroke gait is asymmetric when quantifying foot placement in a body reference frame and this asymmetry related to the hemiparetic walking performance and explained motor control mechanisms beyond those explained by step lengths and step widths alone. We suggest that biomechanical analyses quantifying stepping performance in impaired populations should investigate foot placement in a body reference frame.

Evaluation of the effect of trunk tilt on compressive soft tissue deformations under the ischial tuberosities using weight-bearing MRI - Corrected Proof

Nogah Shabshin, Vlad Ougortsin, Gil Zoizner, Amit Gefen — 2010-02-26

Abstract: Background: Deep tissue injury is the new acceptable term for deep pressure ulcers. Deep tissue injury of the buttocks is typically caused by sustained soft tissue deformations under the ischial tuberosities. Wheelchair users are at high risk, and although usually laterally tilted, the effect of tilts on tissue deformations is unknown. This has brought us to investigate buttocks tissue compressive deformations between the ischial tuberosities and skin during sitting in various body tilts, utilizing weight-bearing Magnetic resonance imaging (MRI).Methods: Ten healthy volunteers underwent sitting MRI, in six postures including neutral with/without weight-bearing, 10° and 20° lateral-tilts, and 20° and 40° anterior tilts. Studies utilized a coronal T1-weighted sequence. Images were evaluated for thickness of tissues between the skin and the lowest point of the ischial tuberosity, of fat between the skin and the gluteus muscle and of muscle between the ischial tuberosity and fat. Measurements in weight-bearing positions were compared to the non-weight-bearing for calculation of compressive tissue deformations in each trunk tilt. Statistical analysis was obtained utilizing multiple pairwise t-tests with Bonferroni corrections.Findings: Muscle and soft tissue compressive deformations, from highest to lowest, were 20°-lateral-tilt (87%, 72%), lateral-10° (85%, 70%), anterior-20° (79%, 67%), anterior-40° (74%, 64%), and neutral (72%, 59%). For the fat, highest was anterior-tilts (42%), followed by lateral-20°-tilt (41%), lateral-10° (39%) and neutral (35%).Interpretation: For lateral tilts, the higher the angle was, the higher the compressive deformation was. However, the most profound change in compressive deformation occurred at the small angle tilts.

Comparison of scapular local coordinate systems - Corrected Proof

2010-02-25

Abstract: Background: Our purposes were to compare between the original and current recommended standard methods of three-dimensional scapular rotation descriptions and to examine the prevalence of gimbal-lock for scapular motion during scapular plane abduction. Additionally we compared these standards to an alternative method and a glenoid based description.Methods: Eleven asymptomatic subjects were studied using electromagnetic sensors secured to bone-fixed pins in the scapula and humerus during two repetitions of scapular plane abduction. Anatomical landmarks defined scapular axes. Scapular angular data were analyzed at humerothoracic elevation angles from initial to maximum elevation. Repeated measures ANOVAs were performed for each variable with a significance level of P<0.05. An anatomical model was used to compare the standards to the alternative and glenoid methods.Findings: For scapular upward rotation and tilting, larger differences occurred between standards at higher angles of elevation. The current standard measured 12.4° less upward rotation and 6.1° greater posterior tilting at maximum elevation as compared to the original. The current standard measured 11.6° less scapular internal rotation across all elevation angles. Using the original landmarks, six subjects attained a mean end-range humerothoracic elevation of 147.4° (SD 12.1°), with a mean end-range scapular upward rotation of 54.4°. The alternative method was more closely aligned to the glenoid method than the current standard.Interpretation: Significant differences were found between the two standards. The current standard interprets the same scapular motion with less internal rotation and upward rotation, and more posterior tilting than the original. No subjects reached upward rotation positions nearing gimbal-lock. Axis orientations also affect clinical interpretation. The alternative method appears worthy of further consideration as shoulder kinematic measurement further evolves.

In situ transverse elasticity and blood perfusion change of sciatic nerves in normal and diabetic rats - Corrected Proof

Rung-Jian Chen, Chou-Ching K. Lin, Ming-Shaung Ju — 2010-02-22

Abstract: Background: Diabetic neuropathy is the most pervasive complication of diabetes mellitus and its etiopathology is not completely elucidated. The existing literature focuses on the histological and structural changes as well as the longitudinal mechanical properties of nerves. The main objective of this study is to investigate the in situ transverse biomechanical properties and changes of microcirculation of sciatic nerves in diabetic and normal control rats.Methods: Quasi-static circular compression experiments were conducted on sciatic nerves of six normal and six diabetic Wistar rats. Local blood perfusion during the compression was also measured by laser Doppler flowmetry. The compressive stress and strain were estimated, in order to calculate the apparent Young’s modulus. The impact of diabetes on peripheral nerves was examined by analyzing the transverse elasticity and microcirculation changes.Findings: The mean transverse apparent Young’s modulus of the sciatic nerves in diabetic rats was 210.7kPa, which was nearly two times greater than that of normal controls (116.3kPa). The pressure threshold that blood perfusion started to decrease in diabetic rats (24.1mmHg) was smaller than in the normal controls (47.1mmHg).Interpretation: These results suggest that the sciatic nerve was stiffer in the diabetic rats. The structural changes in microvessels might lead to earlier decrease of blood perfusion in diabetic nerves under radial compression. These results provide information about the biomechanical and microcirculation changes of peripheral nerves inflicted by diabetes and may also serve as a reference for clinical nerve repair and regeneration for patients with diabetic neuropathy.

Effects of an unstable shoe construction on balance in women aged over 50 years - Corrected Proof

Nerrolyn Ramstrand, Anna Helena Thuesen, Dennis Brandborg Nielsen, David Rusaw — 2010-02-22

Abstract: Background: Shoes with an unstable sole construction are commonly used as a therapeutic tool by physiotherapists and are widely available from shoe and sporting goods retailers. The aim of this study was to investigate the effects of using an unstable shoe (Masai Barefoot Technology) on standing balance, reactive balance and stability limits.Methods: Thirty-one subjects agreed to participate in the study and underwent balance tests on three different occasions. After test occasion one (baseline) 20 subjects received Masai Barefoot Technology shoes and were requested to wear them as much as possible for the remaining eight weeks of the study. Three specific balance tests were administered on each test occasion using a Pro Balance Master (NeuroCom International Inc., Oregon, USA). Tests included; a modified sensory organization test, reactive balance test and limits of stability test.Findings: Subjects in the intervention group significantly improved their performance on elements of all three tests however results on these variables were not demonstrated to be significantly better than the control group. No significant differences were observed across testing occasions in the control group.Interpretation: Results from the present study suggest that, for this group of individuals, use of unstable footwear may improve certain aspects of balance.

Influence of obesity and sarcopenic obesity on plantar pressure of postmenopausal women - Corrected Proof

M. Monteiro, R. Gabriel, J. Aranha, M. Neves e Castro, M. Sousa, M. Moreira — 2010-02-22

Abstract: Background: Menopause is associated with a decrease in fat-free mass and an increase in fat mass. Sarcopenic obesity is more strongly associated with physical limitations than either obesity or sarcopenia and their effect in plantar pressure is not known. Consequently, the scope of the present study was to examine the effect of obesity and sarcopenic obesity on plantar pressure of postmenopausal women, during walking.Methods: Body composition and biomechanics parameters of plantar pressure were assessed in 239 postmenopausal women.Findings: Compared to non-obese and non-sarcopenic women, obese postmenopausal women have higher peak pressure in the metatarsal areas 1, 4, 5, midfoot and lateral heel and higher absolute impulses in all metatarsal and heel areas. On the other hand, sarcopenic obese postmenopausal women presented higher peak pressure and absolute impulses under all metatarsal areas, midfoot and heels. When the absolute values of maximal peak pressures and absolute impulses were normalised to body mass, pressure increases were only perceived for midfoot.Interpretation: The pressure increase found in different foot areas of obese and particularly in sarcopenic obese could cause discomfort and pain in the foot. Sarcopenic obese postmenopausal women also present a higher loading during the stance phase comparing with non-sarcopenic non-obese, fact that might limit their basic daily activity tasks, such as walking.

Proximal humerus fracture rotational stability after fixation using a locking plate or a fixed-angle locked nail: The role of implant stiffness - Corrected Proof

2010-02-16

Abstract: Background: Fixed-angle locked devices have been developed to improve internal fixation of proximal humerus fractures. Available low-profile precontoured locking plates and intramedullary nails with fixed-angle interlocks are currently favored by most surgeons in this setting. The aim of this study was to assess the relative stability of these two methods of fixation under torsion load.Methods: A surgical neck osteotomy was created in six pairs of embalmed humeri. In each pair, one specimen was secured with a titanium locking-compression plate, and the contralateral was secured with a titanium nail with a proximal locked spiral blade. The specimens were first tested cyclically in internal–external rotation for 10,000 cycles to evaluate interfragmentary motion (dynamic study). At the end of the cyclic testing, the specimens were loaded to failure in external rotation to measure torque to failure and construct stiffness (static study).Findings: There were no significant differences in interfragmentary motion between the two fixation devices in the dynamic study. When tested to failure, fixation with the locking plate tolerated on average 20 more degrees in torsion before failure, and demonstrated higher torsional load to failure and less torsional stiffness (P<0.05).Interpretation: Both locking plates and locked intramedullary nails may provide enough stability to avoid secondary displacement of proximal humerus fractures during early physical therapy. Locking plates demonstrated superior biomechanical properties under high rotational loads than locked intramedullary nails in a cadaveric proximal humerus two-part osteotomy model, and could provide more protection against unexpected high torsion loads.

The influence of the axial, antero-posterior and lateral positions of the center of rotation of a ball-and-socket disc prosthesis on the cervical spine biomechanics - Corrected Proof

2010-02-11

Abstract: Background: Previous studies documented the importance of the positioning and the design parameters of the prosthesis in determining the biomechanics of the implanted spine. However, a comprehensive biomechanical evaluation of the significance of these parameters is still lacking. Therefore, the paper is aimed to the quantification of their influence on the flexibility of the implanted spine and the force transmitted through the facet joints.Methods: A finite element model of the C5–C6 spine unit including a ball-and-socket disc prosthesis was built. Three probabilistic variables were considered: the axial, antero-posterior and lateral positions of the center of rotation. Randomized input parameters were generated with the Monte Carlo method. Pure moments of 1.6Nm in flexion, extension, lateral bending and axial rotation were imposed to the upper endplate of C5; 100 simulations were conducted for the each of the considered loading conditions.Findings: Axial position of the center of rotation influenced the spine flexibility in all loading conditions and the facet force in extension, lateral bending and axial rotation. The antero-posterior position was found to influence the spine flexibility in flexion and extension, and the facet force in lateral bending and axial rotation. The lateral position was not significant.Interpretation: The effects of the positioning of a cervical disc prosthesis were estimated. A wide range of mechanical behaviors can be obtained by the manufacturers by appropriately manipulating the position of the center of rotation. A proper positioning of the artificial disc during the surgery, in particular in the antero-posterior direction, was found to be of critical importance.

Patellar tendon repair with hamstring autograft: A cadaveric analysis - Corrected Proof

William M. Mihalko, Matthew Vance, Marc J. Fineberg — 2010-02-04

Abstract: Background: Rupture of the patellar tendon requires surgical repair to restore function of the knee. The most accepted repair technique utilizes running locking non-absorbable sutures secured to the patella through three drill holes. Complications with this repair technique include rerupture, knee stiffness, and extensor lag caused by gap formation at the site of repair. Some surgeons have suggested augmenting the standard repair with local autograft tendon to avoid these complications. It was hypothesized that using a repair technique that included augmentation of the repair with autograft tendons would decrease the gap formation at the repair site under cyclic loading conditions.Methods: In this experiment, eight specimens were used to analyze two methods of patellar tendon repair: hamstrings autograft augmentation and a standard repair using three vertical bone tunnels in the patella. Each specimen was then extended with a 2.2kg weight on the tibia at 0.25Hz to simulate early motion after surgery. The gap formed at the repair site was then measured at 1, 10, 100, and 250cycles and both techniques confidence interval compared using a Wilcoxon signed rank test.Findings: The mean gap formation for the standard repair after one cycle was 8.9mm (SD 2.4) and for the augmented repair was 3.6mm (SD 0.9). At 250cycles the mean gap formed for the standard repair was 13.2mm (SD 1.9) and the mean gap for the augmented repair was 7.2mm (SD 0.9). All gaps for all cycles analyzed had an 88% confidence interval for significance using a Wilcoxon signed rank test.Interpretation: The biomechanical results of this study show statistical trend toward decrease gap formation with an augmented tendon at the repair site under a simulated dynamic knee motion.

Primary stability of custom and anatomical uncemented femoral stems: A method for three-dimensional in vitro measurement of implant stability - Corrected Proof

Per Olav Østbyhaug, Jomar Klaksvik, Pål Romundstad, Arild Aamodt — 2010-02-03

Abstract: Background: Lack of primary stability of cementless hip stems prevents bone ingrowth and may lead to loosening of the stem. Direct measures of the implant stability require drilled holes in the bone at the measuring site. These holes weaken the cortical bone, limit the number of possible measuring points and inhibit other biomechanical measurements. This in vitro study aimed to develop a method for indirect measurement of primary stability of femoral stems, leaving the specimen intact. The method was used to compare the primary stability of two uncemented femoral stems with different proximal fit and fill and different stem length.Methods: An in vitro method for indirect full three-dimensional measurement of implant–bone interface motion was developed. Uncemented customized (n=10) and anatomical stems (n=10) were inserted in human cadaver femora and the primary stability during one leg stance and stair climbing was measured.Findings: The method had high precision, and the errors due to necessary assumption of rigid body components were minimal. The customized stem with optimal proximal fit and fill provided the best initial stability for rotation in retroversion. The anatomical stem with longer stem length was more resistant to permanent rotation in varus.Interpretation: During stem design development the primary stability can be measured at all wanted measuring sites with the presented method, leaving the specimen intact for further analyses.

Nonlinear and anisotropic tensile properties of graft materials used in soft tissue applications - Corrected Proof

Jonathon H. Yoder, Dawn M. Elliott — 2010-02-03

Abstract: Background: The mechanical properties of extracellular matrix grafts that are intended to augment or replace soft tissues should be comparable to the native tissue. Such grafts are often used in fiber-reinforced tissue applications that undergo multi-axial loading and therefore knowledge of the anisotropic and nonlinear properties are needed, including the moduli and Poisson’s ratio in two orthogonal directions within the plane of the graft. The objective of this study was to measure the tensile mechanical properties of several marketed grafts: Alloderm, Restore, CuffPatch, and OrthADAPT.Methods: The degree of anisotropy and non-linearity within each graft was evaluated from uniaxial tensile tests and compared to their native tissue.Findings: The Alloderm graft was anisotropic in both the toe- and linear-region of the stress–strain response, was highly nonlinear, and generally had low properties. The Restore and CuffPatch grafts had similar stress–strain responses, were largely isotropic, had a linear-region modulus of 18MPa, and were nonlinear. OrthADAPT was anisotropic in the linear-region (131 MPA vs 47MPa in the toe-region) and was highly nonlinear. The Poisson ratio for all grafts was between 0.4 and 0.7, except for the parallel orientation of Restore which was greater than 1.0.Interpretation: Having an informed understanding of how the available grafts perform mechanically will allow for better assessment by the physician for which graft to apply depending upon its application.

Three-dimensional stereoradiographic modeling of rib cage before and after spinal growing rod procedures in early-onset scoliosis - Corrected Proof

2010-02-03

Abstract: Background: Early-onset scoliosis frequently leads to major thoracic deformity and pulmonary restrictive disease. Growing rods surgical techniques were developed to achieve a satisfactory correction of the spinal curves during growth. The effect on the rib cage deformity has not yet been documented. The purpose of this study was to analyze the changes of the thoracic geometry after implantation of a growing rod, and to evaluate a stereoradiographic reconstruction method among young scoliotic patients.Methods: Four patients were enrolled in the study, and four additional patients in the reproducibility study. Three-dimensional spine and rib cage models were generated after low-dose stereoradiographic imaging (EOS). Three-dimensional parameters were computed before and after surgery. Intra and inter-observer reproducibility was calculated, and the accuracy was assessed in comparison to volumetric CT-scan.Findings: The average Cobb angle was reduced from 50.8° to 26°. The surgery resulted in a complex 3D effect on the rib cage, combining frontal, lateral, and axial rotation. This effect was dependent of the side (concave or convex), and the position relative to the apical vertebra. Mean errors in comparison to CT-scan were 3.5mm.Interpretation: The results on the spinal deformity are comparable to other series. The effect on the rib cage is of a smaller magnitude than in the case of a spinal arthrodesis. A longer follow-up is necessary to confirm the positive effect on the rib cage deformity. Further research should be performed to improve the reproducibility of 3D parameters.

Biomechanical study of posterior wall acetabular fracture fixation using acetabular tridimensional memory alloy-fixation system - Corrected Proof

Liu Xin-wei, Xu Shuo-gui, Zhang Chun-cai, Fu Qing-ge, Wang Pan-feng — 2010-02-03

Abstract: Background: We developed the acetabular tridimensional memory alloy-fixation system (ATMFS), which is made of NiTi shape memory alloy, according to the specific mechanical properties of biological memory material, nitinol alloy and measured distribution of contact area and pressure between the acetabulum and the femoral head of cadaveric pelvis.Methods: Six formalin-preserved cadaveric pelvis were used for this investigation. Pressure-sensitive film was used to measure contact area and pressure within the anterior, superior, and posterior regions of the acetabulum. The pelvis were loaded under the following four conditions: (1) intact; (2) following a creation posterior wall fracture defect; (3) following reduction and standard internal fixation with reconstruction plate; (4) following reduction and internal fixation with a new shape memory alloy device named ATMFS. A posterior wall fracture was created along an arc of 40–90° about the acetabular rim.Findings: Creation of a posterior wall defect resulted in increased load in the superior acetabulum (1422N) as compared to the intact condition (762N, P=0.007). Following reduction and internal fixation, the load distributed to the superior acetabulum (1486N) was not statistically different from the defect condition. Following the fixation with ATMFS, the load seen at the superior region of the actabulum (936N) was less than fixation with reconstruction plate and was not different from intact state (P=0.4).Interpretation: These data indicate that the use of ATMFS as a fracture internal fixation device resulted a partial restoration of joint loading parameters toward the intact state. ATMFS fixation may result in a clinical benefit.

Biomechanical effects of patellar positioning on intraoperative knee joint gap measurement in total knee arthroplasty - Corrected Proof

2010-02-01

Abstract: Background: Balancing both the lateral/medial and extension/flexion joint gaps is a prerequisite for soft tissue balance in total knee arthroplasty. The purpose of this study was to quantify the effects of patellar positioning and quadriceps load during total knee arthroplasty on knee joint gap measurements.Methods: Eight fresh-frozen cadaveric knees ranging in age from 65 to 85years old were used. Using a medial parapatellar approach, posterior cruciate ligament sacrificing total knee arthroplasty was performed. The specimens were mounted on a custom knee testing system that allowed the femur to be locked in position for knee extension or flexion. Patellar positions of eversion, reduction, and following repair of the arthrotomy were examined. The influence of quadriceps muscle load was investigated by varying the quadriceps load from 0 to 125N. The lateral and medial joint gaps, represented by the distance from the implanted femoral component surface to the cut tibia surface, were measured with 100N tibial distraction force using a 3D digitizer in both extension (0°) and flexion (90°).Findings: Both the medial and lateral joint gaps with patella eversion were significantly smaller than those with patellar reduction and arthrotomy repair (extension: all quadriceps loads, P<0.0002; flexion: quadriceps loads less than 75N, P<0.0002). In patella eversion, quadriceps loading decreased the lateral joint gap more than the medial joint gap in both extension and flexion; however, the effect was greater in knee flexion with significant differences seen at all quadriceps loads, whereas in extension significant differences were only seen for quadriceps loading of 75N and greater. Patella eversion also caused a lateral-posterior shift and external rotation of the tibia compared to the other conditions (P<0.005). With patella reduction and repair of the arthrotomy lower quadriceps loading decreased the extension gap significantly more than the flexion gap (P<0.01). Following repair of the arthrotomy higher quadriceps loading significantly decreased the flexion gap more than the extension gap (P<0.04).Interpretation: The patellar positioning and quadriceps muscle loading in total knee arthroplasty have a strong influence on intraoperative joint gap measurements.

Vibration measurements predict the mechanical properties of human tibia - Corrected Proof

Bekir Bediz, H. Nevzat Özgüven, Feza Korkusuz — 2010-01-28

Abstract: Background: Vibration analysis is a promising technique in diagnosing metabolic bone diseases such as osteoporosis and monitoring fracture healing. The aim of this study is to observe the structural dynamic property changes of the tibia extracted from the vibration analysis data.Methods: In this study, bone mineral density and vibration measurements were made both in in vivo and in vitro conditions. The relationship between structural dynamic properties, obtained and bone mineral densities measured were investigated. Also, the effect of soft tissues on measured structural dynamic properties was analyzed.Findings: Natural frequency of the tibia decreased with decreasing bone mineral density that presented a weak correlation with the bone mineral density values measured by dual energy X-ray densitometer of the femur. In the case of in vitro experiments, it was observed that the effect of muscles on measurement results is higher than that of the effect of the skin and the fibula which makes the modal identification procedure difficult. However, having very large percentage changes in the loss factors when mineral content and collagen are reduced is an encouraging result to believe that damping measurements may yield a promising technique in diagnosing progressing osteoporosis and monitoring fracture healing period.Interpretation: The utilization of natural frequency alone as a diagnosing tool does not seem to be a sufficient method although there is a correlation between this parameter and bone mineral density. However, in vitro experiments showed that the identification of the loss factor is a promising technique in diagnosing progressing osteoporosis.

Upper limb joint dynamics during manual wheelchair propulsion - Corrected Proof

2010-01-27

Abstract: Background: Inverse dynamic methods have been widely used to estimate joint loads during manual wheelchair propulsion. However, the interpretation of 3D net joint moments and powers is not always straightforward. It has been suggested to use joint coordinate systems (expression of joint moment on anatomical axes) and the 3D angle between joint moment and angular velocity vectors (propulsion, resistance or stabilization joint configuration) for a better understanding of joint dynamics.Methods: Nine spinal cord injured subjects equipped with reflective markers propelled in a wheelchair with an instrumented wheel. Inverse dynamic results were interpreted using joint coordinate systems, 3D joint power and the 3D angle between the joint moment and joint angular velocity vectors at the three upper limb joints. The 3D angle was used to determine if the joints were predominantly driven (angle close to 0 or 180 degrees) or stabilized (angle close to 90°).Findings: The wrist and elbow joints are mainly in a stabilization configuration (angle close to 90°) with a combination of extension and ulnar deviation moments and an adduction moment respectively. The shoulder is in a propulsion configuration, but close to stabilization (angle hardly below 60°) with a combination of flexion and internal rotation moments.Interpretation: Stabilization configuration at the joints could partly explain the low mechanical efficiency of manual wheelchair propulsion and could give insight about injury risk at the wrist, elbow and shoulder joints.

Sagittal plane knee joint moments following anterior cruciate ligament injury and reconstruction: A systematic review - Corrected Proof

Joseph M. Hart, Jia-Wei Kevin Ko, Tim Konold, Brian Pietrosimione — 2010-01-25

Abstract: Background: Gait adaptations in persons with anterior cruciate ligament (ACL) injuries have been debated. Many studies examine high speed, 3-dimensional video gait analysis to compare knee joint torques during simulated activities of daily living.Methods: We performed a systematic review of the literature for published clinical papers that reported sagittal plane knee joint kinetics in ACL deficient or reconstructed individuals. We calculated weighted effect sizes (Cohen’s d) to evaluate the magnitude of differences between the injured limb and the contralateral limb and healthy, uninjured limbs in control subjects.Findings: Ten published papers reported kinetic data in ACL deficient subjects while walking for comparisons to the contralateral side (weighted average d=−0.83, range: −3.21, 1.07), and to healthy control knees (weighted average d=−1.0, range: −3.36, 0.17); four papers reported data during jogging compared to the contralateral side (weighted average d=−0.94, range: −4.15, 0.17), and to controls (weighted average d=−1.42, range: −3.83,−0.2). Four papers reported data for ACL-reconstructed patients compared to healthy controls during walking (weighted average d=−0.94, range: −0.4, −1.77) and jogging (weighted average d=−1.18).Interpretation: Effect sizes comparing knee joint moments in injured vs. healthy control subjects appear to be slightly higher while jogging than walking, and higher in ACL-deficient patients compared to reconstructions. However, magnitudes are all large. Few studies report stair climbing. Consequently, it is difficult to make inferences with confidence during these tasks.

Effects of running speed on a probabilistic stress fracture model - Corrected Proof

2010-01-25

Abstract: Background: Stress fractures are dependent on both loading magnitude and loading exposure. Decreasing speed is a potential mechanism of strain reduction during running. However, if running speed is decreased the number of loading cycles will increase for a given mileage. It is unclear if these increased loading cycles are detrimental despite reductions in bone strain. The purpose of this study was to determine the effects of running speed on the probability of tibial stress fracture during a new running regimen.Methods: Ten male subjects ran overground at 2.5, 3.5, and 4.5m/s. Force platform and kinematic data were collected synchronously. Inverse dynamics and musculoskeletal modeling were used to determine joint contact forces acting on the distal tibia. Peak tibial contact force served as input to a finite element model to estimate tibial strains. Stress fracture probability for each running speed was determined using a probabilistic model based on published relationships of bone damage, repair, and adaptation. The effects of speed on stress fracture probability was compared using a repeated measures ANOVA.Findings: Decreasing running speed from 4.5 to 3.5m/s reduced the estimated likelihood for stress fracture by 7% (P=0.017). Decreasing running speed from 3.5 to 2.5m/s further reduced the likelihood for stress fracture by 10% (P<0.001).Interpretation: Runners wanting to reduce their risk for tibial stress fracture may benefit from a decrease in running speed. For the speeds and mileage relative to the current study, stress fracture development was more dependent on loading magnitude rather than loading exposure.

How do visual, spectroscopic and biomechanical changes of cartilage correlate in osteoarthritic knee joints? - Corrected Proof

2010-01-22

Abstract: Background: Characteristic changes in cartilage of human knee joints with different degrees of osteoarthritis (OA) have been investigated by visual, biophotonical and biomechanical examination. Knowledge about the cartilage composition and changes during the development of OA is important for diagnostic decisions and understanding the pathogenesis of OA.Methods: Thirty two patients with severe knee OA received endoprosthetic replacement. During surgical intervention cartilage specimen were harvested from defined surface areas of the joints. The degree of cartilage defects was classified visually (ICRS Grade: International Cartilage Repair Society), biophotonically (NIRS: near infrared spectroscopy) and biomechanically (Young’s Modulus). To characterise links between the investigated parameters the Spearman’s rank correlation coefficient was used.Findings: Significant negative correlations were found between visual macroscopic degree of degeneration (ICRS Grade) and biophotonic characteristics (NIRS) (ρ=−0.467) or cartilage stiffness (Young’s Modulus) (ρ=−0.501). Between NIRS and Young’s Modulus significant positive correlation of ρ=0.535 was detected.Interpretation: Visual, biophotonic and biomechanical properties of cartilage reveal strong correlations in all degrees of cartilage defects in patients with severe OA. According to these results, we indicate that an objective, non-invasive and non-destructive measurement of cartilage properties during open and arthroscopic knee surgery is possible by NIRS and provide a novel tool to evaluate disease intervention and treatment.

Fixed-angle plate osteosynthesis of the patella – An alternative to tension wiring? - Corrected Proof

M. Wild, C. Eichler, S. Thelen, P. Jungbluth, J. Windolf, M. Hakimi — 2010-01-22

Abstract: Background: The goal of this study is carry out a biomechanical evaluation of the stability of a bilateral, polyaxial, fixed-angle 2.7mm plate system specifically designed for use on the patella. The results of this approach are then compared to the two currently most commonly used surgical techniques for patella fractures: modified anterior tension wiring with K-wires and cannulated lag screws with anterior tension wiring.Methods: A transient biomechanical analysis determining material failure points of all osteosyntheses were conducted on 21 identical left polyurethane foam patellae, which were osteotomized horizontally. Evaluated were load (N), displacement (mm) and run-time (s) as well as elastic modulus (MPa), tensile strength (MPa) and strain at failure (%).Findings: With a maximum load capacity of 2396 (SD 492) N, the fixed-angle plate proved to be significantly stronger than the cannulated lag screws with anterior tension wiring (1015 (SD 246) N) and the modified anterior tension wiring (625 (SD 84.9) N). The fixed-angle plate displayed significantly greater stiffness and lower fracture gap dehiscence than the other osteosyntheses. Additionally, osteosynthesis deformation was found to be lower for the fixed-angle plate.Interpretation: A bilateral fixed-angle plate was the most rigid and stable osteosynthesis for horizontal patella fractures with the least amount of fracture gap dehiscence. Further biomechanical trials performed under cycling loading with fresh cadaver specimen should be done to figure out if a fixed-angle plate may be an alternative in the surgical treatment of patella fractures.

A comparison of the quasi-static mechanical and non-linear viscoelastic properties of the human semitendinosus and gracilis tendons - Corrected Proof

Steven D. Abramowitch, Xiaoyan Zhang, Molly Curran, Robert Kilger — 2010-01-21

Abstract: Background: Over 50-% of anterior cruciate ligament reconstructions are performed using semitendinosus and gracilis tendon autografts. Despite their increased use, there remains little quantitative data on their mechanical behavior. Therefore, the objective of this study was to investigate the quasi-static mechanical and non-linear viscoelastic properties of human semitendinosus and gracilis tendons, as well as the variation of these properties along their length.Methods: Specimens were subjected to a series of uniaxial tensile tests: 1-h static stress-relaxation test, 30 cycle cyclic stress-relaxation test and load to failure test. To describe the non-linear viscoelastic behavior, the quasi-linear viscoelastic theory was utilized to model data from the static stress-relaxation experiment.Findings: The constants describing the viscoelastic behavior were similar between the proximal and distal halves of the gracilis tendon. The proximal half of the semitendinosus tendon, however, had a greater viscous response than its distal half, which was also significantly higher than the proximal gracilis tendon. In terms of the quasi-static mechanical properties, the properties were similar between the proximal and distal halves of the semitendinosus tendon. However, the distal gracilis tendon showed a significantly higher tangent modulus and ultimate stress compared to its proximal half, which was also significantly higher than the distal semitendinosus tendon.Interpretation: The results of this study demonstrate differences between the semitendinosus and gracilis tendons in terms of their quasi-static mechanical and non-linear viscoelastic properties. These results are important for establishing surgical preconditioning protocols and graft selection.

The association between external-ground-reaction force and knee-joint kinetics during partial- and full-weight-bearing gait - Corrected Proof

Jay R. Ebert, David G. Lloyd, Anne Smith, Timothy Ackland, David J. Wood — 2010-01-21

Abstract: Background: Progressive weight-bearing is recommended following autologous chondrocyte implantation. This weight-bearing program assumes that increasing external loads experienced at the foot during gait are closely related to external-knee-joint moments. We investigated this relationship, and examined other variables that may contribute to knee-joint kinetics of which the clinician can modify using practical instruction within a clinical setting.Methods: Gait analysis was performed in 51 patients following autologous chondrocyte implantation, during various partial- and full-weight-bearing conditions. The contribution of ground-reaction force, kinematic and spatio-temporal gait parameters to external-knee moments was investigated within weight-bearing levels less than 60%, between 60% and 90% and more than 90% of individual body weight.Findings: There was no association between peak-ground-reaction force and the knee-adduction moment within the 60–90% and more than 90% weight-bearing conditions, nor the peak-knee-flexion moment at less than 60% weight-bearing. Peak-ground-reaction force accounted for no more than 21.4% and 18.6% of the variance in the knee-adduction and flexion moments, respectively, within any weight-bearing condition, while the combination of peak-ground-reaction force, kinematic and spatio-temporal parameters investigated accounted for no more than 39.7% and 52.2%, respectively. Foot-progression angle and knee-flexion during weight acceptance accounted for a significant (P<0.05) portion of the variance in external-knee moments, particularly at higher levels of weight-bearing.Interpretation: A large amount of variance in knee moments may be attributed to variables other than external loads, some of which can be modified by the clinician. Clinically, this is important for any therapist implementing progressive weight-bearing protocols.

Mechanical properties of glenoid cancellous bone - Corrected Proof

2010-01-18

Abstract: Background: Loosening of the glenoid component in total shoulder arthroplasty is the main late complication of this procedure; it may be assumed that it is highly dependent on the quality of the glenoid cancellous bone. Very little is known about the mechanical properties of this cancellous bone. The aim of this study was to determine these properties (Young’s modulus and strength) as well as bone density in different parts of the glenoid cancellous bone to assess their variations.Methods: Eleven scapulas were obtained from six fresh-frozen, unembalmed human cadavers. Eighty-two cubic cancellous bone specimens were extracted and tested using a uniaxial compression test; then the specimens were defatted and correlations with bone density were determined.Findings: The study showed significant differences in the mechanical properties with anatomic location and directions of loading. Young’s modulus and strength were found to be significantly higher at the posterior part of the glenoid with the weakest properties at the antero-inferior part. Cancellous bone was found to be anisotropic with higher mechanical properties in the latero-medial direction perpendicular to the articular surface of the glenoid. The apparent density was on average equal to 0.29g/cm3 with the higher values at the posterior and superior part of the glenoid. Good correlation between apparent density and elastic modulus was found only in the sagittal planes but not in the coronal and axial plane.Interpretation: The mechanical properties determined in this study showed the anisotropy of the glenoid cancellous bone; values of these properties could provide input data for finite element method analyses in shoulder prosthesis designs.

Gait parameters and stride-to-stride variability during familiarization to walking on a split-belt treadmill - Corrected Proof

Joseph A. Zeni, Jill S. Higginson — 2009-12-10

Abstract: Background: Subjects unfamiliar to walking on a split-belt treadmill may initially demonstrate an altered gait pattern or increased variability of gait parameters. While previous investigations have examined kinematic variables associated with familiarization time, the objective of this study was to determine the familiarization period required to obtain the most reproducible gait pattern through the assessment of kinetic, kinematic and spatio-temporal parameters during a single session of treadmill walking.Methods: Eleven healthy subjects participated in a single bout of treadmill walking which lasted 9min. Kinematic and kinetic data were collected from the first 30s of each minute, beginning when the treadmill reached full speed. Means and standard deviations for knee flexion at heel strike, ground reaction forces, step width and step length were obtained to examine the changes in each variable over the 9min. Mean r2 values were evaluated for changes in variability from one stride to the subsequent stride for sagittal plane hip, knee and ankle joint angles and moments, as well as for vertical and horizontal ground reaction forces.Findings: Significant reductions in variability were found for vertical and horizontal ground reaction forces, knee flexion at heel strike and step length over 9min. Only step width showed a change in the mean value across trials. There were no increases in r2 values after the 5th min for any of the gait variables.Interpretation: The results suggest that in order to collect accurate data for gait analysis, subjects should be familiarized to the split-belt treadmill for at least 5min prior to data collection.